1. Field of the Invention
The present invention relates to a design and method of fabrication for an RF line replaceable module (LRM) utilizing a "building block" fabrication approach of composite material moldings for use in future avionic systems.
2. Description of the Prior Art
To date, airborne radio frequency (RF) modules have been composed of aluminum blocks machined to specific internal and external configurations. The weight of the RF module is a critical factor because their applications usually involve advanced avionics where weight of the critical radar components must be maintained to a minimum.
In electronic applications such as airborne or aerospace electronics, specifically radar systems, it is highly desirable to minimize the weight of the thermal transfer means utilized in these systems.
Aluminum is relatively light weight--0.1 lb/in.sup.3. However, the defense applications and demand for lightweight avionics require the utilization of composite materials for Standard Electronic Modules (SEM). The thermal integrity of the mounting surfaces of these thermal planes for avionics use must be maintained. Therefore, a molded composite thermal plane of pitch based carbon fiber having unique heat conductive properties would preserve the thermal integrity of the mounting surfaces without undue weight. A weight reduction of potentially thirty-five percent could be expected per unit.
The problem to be solved then is the design and fabrication of an RF line replaceable module or standard electronic module having extremely light weight while maintaining thermal integrity.
The trend for the next generation of LRMs is to continue minimizing weight and unit costs. It is therefore important to think in terms of standardizing composite moldings and specializing only in those portions requiring specific designs. The concept as addressed by this invention implements an RF module having three standard composite moldings which significantly reduces material weight, improves thermal performance, as well as overall unit cost.
It is standard practice in existing electronic systems to utilize as a thermal transfer means a conductive thermal plane with printed circuit boards mounted upon it. The printed circuit boards are mounted with heat generating electronic components which require heat dissipation. Such heat dissipation via a conductive thermal plane makes use of plates of aluminum or copper having one or more printed circuit boards mounted upon it. The thermal plane interfaces with a heat sink contacting and conducing heat to the edges of the thermal plane.
A thermal transfer means as seen in U.S. Pat. No. 4,602,678, entitled "Interfacing of Heat Sinks With Electrical Devices And The Like," issued July 29 1986 to inventor Herbert J. Fick, is described as a silicon layer with embedded thermally conductive metal oxides.
In a recently issued patent, U.S. Pat. No. 4,730,232 entitled "High Density Microelectronic Packaging Module for High Speed Chips", as owned by the assignee of the present invention, an aluminum thermal plane for cooling printed circuit board attachments as positioned on opposing sides of the thermal plane in a standard electronic module is described.
Further, the utilization of composite heat transfer material such as P-100, a pitch based carbon fiber in a matrix such as an epoxy as seen in issued U.S. Pat. No. 4,849,858 entitled "Composite Heat Transfer Means" is known in the art. This patent, owned by the assignee of the present invention, describes a thermal heat transfer member comprising a planar composite utilizing thermally conductive graphite fibers disposed within a matrix material. That invention, "Composite Heat Transfer Means", was usable in a variety of applications ranging from the SEM embodiment with a composite heat transfer member bonded between circuit board laminates, to a more generic thermal plane electronic application for use as a heat transfer member wherein one part of an electronic chassis or RF module.